2 Note: A salt bridge can be used in the Electrolytic Cell Look for reversal of charge (anode is positive and cathode is negative). energy is supplied 2. Example: Consider the spontaneous electrochemical cell: Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) E o cell = + V. If instead this cell was connected to an external electric source of voltage greater than V then the reverse reaction could take place. That is, electrons would be forced into the zinc electrode and removed from the copper electrode. The net reaction taking place in the Electrolytic cell is the reverse of that taking place in the electrochemical cell, and the resulting E ocell is negative. Cu (s) Cu2+(aq) + 2e- EoCu2+/Cu = - V oxidized anode Zn2+(aq) + 2e- Zn(s) o E Zn2+/Zn = - V reduced cathode _____. Cu(s) + Zn2+(aq) Cu2+(aq) + Zn(s) E o cell = - V.

3 Recall that the anode and the cathode are assigned based on the half reactions that are taking place at the electrode surface. LEOA (Loss of Electrons Oxidation Anode) Oxidation always occurs at the anode. In an electrochemical cell electrons are freed at the anode, hence it is (-). In an Electrolytic cell electrons are withdrawn from the anode, hence it is (+). GERC (Gain of Electrons Reduction Cathode) Reduction always occurs at the cathode. In an electrochemical cell electrons are removed by the reduction half reaction, hence the cathode is (+). In an Electrolytic cell electrons are forced into the cathode, hence it is (-). 3. Electrolysis of Water Pure water cannot carry a current. In order to decompose H2O via Electrolysis , some electrolyte, like KNO3 or H2SO4, must be added in low concentrations.

9 2. The development of electroplating (Micheal Faraday). Electroplating is the process in which a metal is deposited (plated) onto the cathode of an Electrolytic cell. It's used to protect the surface of the base metal or to make the object more attractive. 3. The purification of impure metals Electrowinning is used to produce very pure sodium and other reactive metals from Electrolysis of molten salts Electrorefining is used to obtain ultra-pure silver, lead and copper from the Electrolysis of impure solid metal 8. Electrolysis WORKSHEET #6. 1. The Electrolysis of molten calcium chloride produces calcium and chlorine. Write the half- reaction that takes place at the anode and the half-reaction that takes place at the cathode. Also, write the overall cell reaction for this process. 2. An Electrolytic cell containing one half-cell consisting of a nickel electrode in a 1 mol/L nickel (III) chloride solution and the other half-cell consisting of a cadmium electrode in a 1 mol/L.

10 Cadmium chloride solution is assembled. (a) Sketch the cell and label the anode, the cathode, and the direction of electron flow. Be sure to include a salt bridge and a power supply in your sketch. (b) Find the cell potential. (c) Write the oxidation half-reaction, the reduction half-reaction and the overall cell reaction. d) Explain how the Electrolytic cell works. 3. What would be the minimum voltage to operate the following cell: Ag(s)|Ag+(aq) || Cu2+(aq)|Cu(s). 4. Predict whether the following reactions would be spontaneous or non-spontaneous. (a) Br2(aq) + 2 I-(aq) I2(aq) + 2Br - (aq). - (b) I2(aq) + 2Br (aq) Br2(aq) + 2 I-(aq). (c) Cl2(aq) + 2 I-(aq) I2(aq) + 2Cl- (aq). (d) I2(aq) + 2Cl- (aq) Cl2(aq) + 2 I-(aq). 5. Which of the following reactions occurs spontaneously and which can only be brought about through Electrolysis , assuming that all reactants and products are in their standard states?